Idle is high after TB install
Thread Starter
11 Second Club
Joined: Apr 2002
Posts: 526
Likes: 0
From: Waldorf, MD
Idle is high after TB install Put on a ported TB today, and now my idle is high. It normally runs about 500rpms, but now it's around 1,000rpm. Not only that, but it's like it has cruise control on all the time now. I'll be driving along at 30mph, take my foot off the gas, and it'll stay consistant 
Something wrong?
Something wrong?
Originally Posted by Raptor99
Put on a ported TB today, and now my idle is high. It normally runs about 500rpms, but now it's around 1,000rpm. Not only that, but it's like it has cruise control on all the time now. I'll be driving along at 30mph, take my foot off the gas, and it'll stay consistant Something wrong?
Something wrong?Brandon
Make sure the idle stop screw is backed out enough
to seat it, and that you do not see daylight past the
blade when closed ("lumpy" daylight would mean the
port-job munged the seating circle). But I think that
"cruise control" more likely means vacuum leak (check
the TB-manifold O-ring), overdrilled hole, cables too
tight (hanging the TB slightly open) of crap in the IAC
that keeps it from seating. Seems to be a high incidence
of plain bad IAC motors when dealing with the fancy
powder-coated "professional" TBs. Might swap your
old IAC servo on after blowing out the IAC bore and
checking the seating circle for crud.
to seat it, and that you do not see daylight past the
blade when closed ("lumpy" daylight would mean the
port-job munged the seating circle). But I think that
"cruise control" more likely means vacuum leak (check
the TB-manifold O-ring), overdrilled hole, cables too
tight (hanging the TB slightly open) of crap in the IAC
that keeps it from seating. Seems to be a high incidence
of plain bad IAC motors when dealing with the fancy
powder-coated "professional" TBs. Might swap your
old IAC servo on after blowing out the IAC bore and
checking the seating circle for crud.
Make sure the idle stop screw is backed out enough
to seat it, and that you do not see daylight past the
blade when closed ("lumpy" daylight would mean the
port-job munged the seating circle). But I think that
"cruise control" more likely means vacuum leak (check
the TB-manifold O-ring), overdrilled hole, cables too
tight (hanging the TB slightly open) or crap in the IAC
that keeps it from seating. Seems to be a high incidence
of plain bad IAC motors when dealing with the fancy
powder-coated "professional" TBs. Might swap your
old IAC servo on after blowing out the IAC bore and
checking the seating circle for crud.
to seat it, and that you do not see daylight past the
blade when closed ("lumpy" daylight would mean the
port-job munged the seating circle). But I think that
"cruise control" more likely means vacuum leak (check
the TB-manifold O-ring), overdrilled hole, cables too
tight (hanging the TB slightly open) or crap in the IAC
that keeps it from seating. Seems to be a high incidence
of plain bad IAC motors when dealing with the fancy
powder-coated "professional" TBs. Might swap your
old IAC servo on after blowing out the IAC bore and
checking the seating circle for crud.
TECH Addict
Joined: Feb 2004
Posts: 2,826
Likes: 0
While we are on the high idle subject, if your idle is high beyond the IACs capability to adjust, will the PCM pull the maximum amount of ignition timing that it is allowed in order to try and bring the idle down?
Just back-off the idle set screw and slam the thing closed a few times. Do this until it sticks and then give it a 1/4 turn back in. Be sure to reset the comp by pulling your negative. Either the person who ported the unit didn't do this before sending it off, or the person you bought this from screwed with it.
I bored hundreds of units for all makes and models a couple yrs back. Every now and again, one would slip through the seat test. Just one of those hard to 'see' details.
I bored hundreds of units for all makes and models a couple yrs back. Every now and again, one would slip through the seat test. Just one of those hard to 'see' details.
Trending Topics
Thread Starter
11 Second Club
Joined: Apr 2002
Posts: 526
Likes: 0
From: Waldorf, MD
I just talked to the guy I got it from, and it sounds like I need to twist the screw in a little more, because he backed it out a tad to compensate for his cam. Just in case that's not enough though, how do you loosen the throttle cable?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
No no no, not twist in, twist out. You want to loosen the screw to let the blade close more, you don't want to open it more. That's what's causing your high idle. The guy must have tightened (turned in) the set screw to compensate for the cam. If he had backed off from the factory setting, it'd provide less air, or just stick when shut quick. You're backwards...
Thread Starter
11 Second Club
Joined: Apr 2002
Posts: 526
Likes: 0
From: Waldorf, MD
Originally Posted by NoseUpChromeDown
No no no, not twist in, twist out. You want to loosen the screw to let the blade close more, you don't want to open it more. That's what's causing your high idle. The guy must have tightened (turned in) the set screw to compensate for the cam. If he had backed off from the factory setting, it'd provide less air, or just stick when shut quick. You're backwards...
I got everything worked out though. One and a half turns got me around 600RPMs again for idle. Had to reset the PCM fuse though to ditch the code. Thanks for all the help guys!
Originally Posted by Raptor99
Yeah, my bad. I knew what to do, just worded it wrong
I got everything worked out though. One and a half turns got me around 600RPMs again for idle. Had to reset the PCM fuse though to ditch the code. Thanks for all the help guys!
I got everything worked out though. One and a half turns got me around 600RPMs again for idle. Had to reset the PCM fuse though to ditch the code. Thanks for all the help guys!
